Bismaleimide resin systems toughened by addition of preformed functionalized low Tg elastomer particles

ABSTRACT

Bismaleimide resin systems and fiber reinforced prepregs prepared therefrom having exceptional toughness are prepared by dispersing into a bismaleimide base resin system preformed functionalized elastomer particles having a T g  of less than 10° C.

This application is a continuation of application Ser. No. 07/756,001filed Sep. 6, 1991, now abandoned, which was a continuation-in-part ofapplication Ser. No. 07/738,006, filed Jul. 30, 1991 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the field of fiber-reinforcedthermosetting composites. More particularly, the invention pertains tofiber-reinforced prepregs containing thermosetting bismaleimide resinsystems containing particulate, functionalized elastomers having a T_(g)of 10° C. and below, and the composites prepared therefrom.

2. Description of the Related Act

The use of fiber-reinforced thermoset composites continues to grow.While great strides have been made in increasing the strength,toughness, temperature use ceiling, and other important physicalproperties, improvement is still required. Although some resin systems,e.g. the bismaleimides, offer high use temperatures, epoxy resin systemsremain the system of choice for many applications. Cyanate resin systemsalso are preferred for some applications.

However, all these resin systems are somewhat brittle, and thus easilysubject to impact-induced damage. This lack of toughness has limitedtheir use to non-critical applications, e.g. in sporting goods equipmentand for non-load bearing applications in the transportation andaerospace industries. Many methods of increasing toughness of such resinsystems have been investigated. As one result of such investigations,numerous new epoxy resin monomers have been introduced into the market.However despite initial promise, the use of these new and often highercost epoxy monomers has not resulted in the increase in the toughnessdesired in composites. Bismaleimide resin systems are oftencopolymerized with unsaturated compounds such as diallylbisphenol A forthe same reason.

What has become clear from the many investigations is that it is notpossible, in general, to predict composite properties based on neatcured resin data, and as a result, air frame manufacturers insist thattoughness be assessed on cured composite panels.

Other efforts to improve resin toughness has been the inclusion ofsoluble thermoplastics or elastomers into the resin system. For example,dissolution of polyethersulfone thermoplastics to epoxy resins wasdisclosed by Bucknall and Partridge in the British Polymer Journal, v.15, March 1983 pages 71-75. The systems demonstrating the greatesttoughness developed a multiphase morphology upon cure. U.S. Pat. No.4,656,208 discloses a similar multiphase system wherein a reactivepolyethersulfone oligomer and an aromatic diamine curing agent react toform complex multiphase domains. However, the systems of Bucknall havevery high viscosities due to requiring excessive amounts of dissolvedthermoplastic, and yet still do not meet the desired toughnessstandards. The systems of U.S. Pat. No. 4,656,208 are capable ofpreparing composites of good toughness, but are difficult to prepare andto process. In particular, the morphology is very cure-cycle dependent,and variations in the cure cycle may greatly affect the toughness of thecured composite.

The addition of soluble, reactive elastomers is known to increasetoughness of epoxy resins, and has been used successfully in epoxyadhesives. However, the addition of soluble elastomers to epoxies foruse in fiber-reinforced composites results in a decrease in modulus,strength, and use temperature.

The use of rigid particles to toughen epoxy resins is disclosed inEuropean published application EP-A-O 274 899 where transparentinfusible nylon particles when added to epoxy resins which when curedproduce an interpenetrating network created an increase in compositetoughness, and in European published application EP-A-252725 wherefillers of glass and polyvinyl chloride were added to epoxy resinformulations, although the latter appeared to exhibit no increase intoughness as a result of such addition.

In European application EP-A-0 351 027 published Jan. 17, 1990 and inU.S. Pat. Nos. 4,977,218 and 4,977,215, the use of high T_(g)particulate carboxylated crosslinked elastomers having shore hardness ofgreater than Shore D50 are said to increase toughness of epoxyresin-based composites. However, it is stated that the particles mustremain rigid and perform, in addition to other functions, the functionof maintaining ply separation. It is further stated that in order toperform this function, that softer elastomers, or those having a T_(g)of less than 15° C. will not work. However, it is undesirable toincrease interlaminar separation excessively, as this increasedthickness of the interlaminar region requires a greater amount of matrixresin. As a result, the volume percent of fiber-reinforcement isdecreased and the composite, while being tough, loses strength andmodulus. Furthermore, it has been found that such particulate elastomerscompletely fail to increase toughness of brittle epoxy resin matrices.

U.S. Pat. No. 4,999,238 discloses a multiphase epoxy resin compositioncontaining infusible particles which in turn contain carboxylfunctionalelastomers. These compositions are prepared by polymerizing an epoxyresin, a diamine curing agent, e.g. diaminodiphenylsulfone, a reactivepolyethersulfone oligomer, and a solution of an elastomer such as B. F.Goodrich Hycar® 1472. During cure, infusible particles ofepoxy/hardener/oligomer/elastomer phase separate, these particlesfurther containing domains of elastomer. However, such multiphasicsystems are difficult and expensive to prepare and also difficult toprocess. Preparation involves multiple process steps which involve useof expensive, functionalized, soluble polyethersulfone oligomers whichincrease resin system viscosity undesirably. In addition, such systemsare subject to unpredictable changes in morphology due to variations inresin processing, cure temperature, and cure cycle.

The same approaches to toughening epoxy resin matrices have also beenattempted with other thermosetting resins, with some degree of success.It has been found, however, that often the methods successful intoughening epoxy resins fail with respect to bismaleimide or cyanateresins. An example is the use of particulate thermoplastic polyimide2080 available from Lenzing AG and Matrimide 5218 thermoplasticpolyimide available from Ciba-Geigy. The former was ineffective intoughening epoxy resin matrices but very effective in bismaleimides,while the latter was highly effective in epoxy resins but much lesseffective in bismaleimides. Therefore, it would be desirable to discovera method of toughening which is to some degree formulation independent.

SUMMARY OF THE INVENTION

It has now been surprisingly discovered that thermosetting bismaleimidefiber-reinforced composites may be toughened against impact induceddamage by incorporation of a most minor amount of preformedfunctionalized elastomer particles having a T_(g) of less then 10° C.and a particle size from 2 μm to 70 μm into the uncured matrix resinsystem of the fiber-reinforced prepregs used to prepare such composites.Preferably the base resin system (less the functionalized elastomer) iscapable of producing a composite having a compression strength afterimpact (CAI) of 22 Ksi or more.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The base resin systems useful in the subject invention are derived frombismaleimide resins. By the term "bismaleimide" as used herein is alsomeant the closely related nadicimides. Preferred bismaleimides are thebismaleimides and nadicimides of toluenediamine, aliphatic amines,methylenedianiline, aliphatic diamines, isophorone diamine, and thelike. Further examples of suitable bismaleimides are disclosed in U.S.Pat. Nos. 4,644,039 and 5,003,018 which are herein incorporated byreference. Generally, the bismaleimides are copolymerized with analkenylphenol comonomer such as o,o'-diallylbisphenol A,o,o'-diisopropenylbisphenol A, allyleugenol, etc. When bismaleimides arethe major thermosetting resin it is frequently desirable to add a lowviscosity epoxy resin, for example a bisphenol F epoxy or resorcinolbased epoxy to the resin system in minor amount. Further suitable lowviscosity epoxy resins are disclosed on pages 14-16 of copending U.S.application Ser. No. 07/413,429 which is herein incorporated byreference.

The cyanate resins are also well known, and may be prepared by reactinga cyanogen halide, preferably cyanogen bromide, with a phenol to formthe corresponding cyanate ester. Suitable cyanates are those preparedfrom resorcinol, the bisphenols, particularly bisphenol A and bisphenolF, the phenolated dicyclopentadienes, dihydroxynaphthalenes, anddihydroxybiphenyls. The cyanate resins may be used in conjunction withbismaleimide resins.

It is preferred that the resin system chosen have a base resin CAI ofgreater than 22 Ksi. By this it is meant that the base resin, less lowT_(g) functionalized elastomer particles, and not including particulatethermoplastic tougheners, when used to impregnate intermediate modulusunidirectional carbon fibers such as Hercules IM-7 or Celion G-500fibers, and then consolidated into a quasiisotropic panel in accordancewith Boeing Support Specification BSS 7260 will have a compressionstrength after 1500 inch-lb/in impact of 22 Ksi or more. Although thistest of neat resin toughness is measured on intermediate modulus fibers,it should be emphasized that the resin systems, having met this test,may be utilized with any reinforcing fibers including but not limited tohigh and low modulus as well as intermediate modulus carbon fibers.

The particulate modifiers employed in the practice of this invention maybe characterized as comprising preformed, functionalized, low T_(g)particles, and more particularly as being a finely-divided,functionalized, partially cross-linked rubber. Particles formed ofcarboxylated and amino and anhydride functionalized rubbers exhibitparticularly good adhesion to the matrix resin, possibly by becomingchemically bound to the matrix resin or simply by having an improvedaffinity for the matrix resin due to the presence of polar groups at theparticle surface.

The particles are further characterized as being partially crosslinked,meaning that the rubber particles will exhibit sufficient integrity toresist being solubilized appreciably at temperatures that will normallybe encountered during the fabricating and curing of the laminate. Suchrubber particles will be dispersed in the matrix resin withoutdissolving or otherwise losing their particulate character. Rubbershaving glass transition temperatures below 10° C., preferably below 0°C. are suitable.

Suitable functionalized rubbers include conventional diene and olefinrubbers having, or modified to include, from about 0.1 to about 5 wt %,preferably from about 0.5 to about 3 wt % carboxyl, carboxamide,anhydride, epoxy, or amine functionality. The particular functionalgroups should be capable of reacting with at least one of the resinsystem monomers. Representative of such diene rubbers are the variety ofwell known rigid, possibly cross-linked copolymers of butadiene orisoprene including for example the dieneacrylonitrile copolymers widelyavailable as nitrile rubbers, copolymers of vinyl aromatic monomers anddiene monomers such as the styrene-butadiene copolymers known as SBRrubbers, and terpolymers of dienes with acrylonitrile and styrene orvinyl toluene, all of which, when modified with the desired level offunctionality, may be described as functionalized diene rubbers. Manysuch rubbers having T_(g) values below 10° C. and preferably below 0° C.and the desired functionality are readily available from commercialsources. Also useful are rubbery copolymers of acrylate esters withcarboxyl functionality, which may be described as carboxylated acrylicrubbers. Acrylic rubbers with the desired level of carboxylicfunctionality and having T_(g) values in the range of -25° C. to 10° C.are also commercially available in a variety of forms. Other polymerswhich may be similarly modified to include carboxyl or otherfunctionality include rubbery copolymers and particularly graftcopolymers of styrene, vinyltoluene or the like and optionally one ormore additional copolymerizable vinyl monomers on a rubbery polymericsubstrate, using a sufficiently high level, preferably greater than 60wt %, of the rubbery substrate component. Specific examples includerubbery acrylonitrile-butadiene-styrene (ABS) polymers,methylmethacrylate-butadiene-acrylonitrile-styrene (MABS) polymers andthe like.

Modification of rubbers to include carboxyl functionality may beaccomplished by a variety of well known processes, includingcopolymerizing the rubber monomers with a suitable copolymerizablecarboxylic monomer or by grafting the preformed rubber in solution,suspension, or latex form, with carboxylic compounds such as maleicanhydride, maleimide, acrylic acid, itaconic acid or the like. Othermethods for providing carboxylated rubbery polymers having the necessarycharacter include grafting the polymers in particle form with mixturesof a monomer and a copolymerizable carboxylic or other functionalunsaturated compound to provide particles having a relatively rigidouter shell with reactive carboxylic or other functionality, and manysuch core-shell particulate modifiers are also known and commerciallyavailable. Also suitable are post reaction processes for functionalizingrubbery diene copolymers, olefin rubbers and the like, as recentlydescribed in U.S. Pat. Nos. 4,740,552 and 4,654,405.

The functionalized rubbers suitable for use as rubber particlesaccording to the practice of this invention may thus be described asfunctionalized rubbers having a T_(g) less than 10° C. which may beselected from the group of functionalized diene rubbers, functionalizedacrylic rubbers, and mixtures thereof.

The functionalized rubber particles may be solid, porous or hollow andtake any convenient shape, and may for example be formed into bead-likespheres or oblate spheroids from solutions, dispersions or suspensionsof the rubber by a variety of processes including spray drying, flashevaporation, precipitation, coagulation or the like. The particles mayalso be produced from bulk material by a pulverizing or grindingprocess, optionally under cryogenic conditions, to provide particlesrough and irregular in shape. Suitable particles may also be formed bycoating a functionalized rubber onto a particulate support having theappropriate size then partially cross-linking the carboxylated rubbercoating. For example, SAN and polyolefin resins, as well as SBR, nitrilerubber and the like are available as particles in the form of a latex,suspension or dispersion. Such particles may be coated individually witha functionalized rubber together with appropriate curing additives,cured to form a cross-linked coating on the individual particles, thencollected in particle form by a spray-drying operation or the like.

Amino-functionalized elastomers may be prepared by known methods, andare disclosed, in the article "Elastomer-Modified Epoxy Resins inCoatings Applications" by R. S Drake, et. al., Epoxy Resin Chemistry II,Bauer, Ed., ACS Symposium Series 221, ©1983, pp 1-20. Anhydridefunctional elastomers are also useful. These may be prepared, forexample, by including maleic anhydride in the mixture of monomers usedto prepare the elastomers.

The particle size of the functionalized elastomers should be in therange of 2 μm to 70 μm, preferably 5 μm to 50 μm. The weight percentageof functionalized elastomer in the resin system is most minor, generallybeing less than 10 percent by weight. Amounts of from 3 weight percentto 8 weight percent have been found to be particularly useful.

In mixing the resin system ingredients and particulate elastomer, careshould be taken to assure that the low T_(g) preformed functionalizedelastomer particles remain in particulate form, i.e. no appreciablesolution into the resin system components takes place. This canordinarily be achieved under normal resin mix conditions, although withsome elastomers, the mixing temperature or time may have to be lowered.Such modifications to normal mix conditions are within the level ofskill in the art. Light crosslinking of the rubber particles facilitatesthis requirement.

The single phase systems of the subject invention may further contain aparticulate engineering thermoplastic. Such thermoplastics have highstrength and glass transition temperatures above 150° C., preferablyabove 200° C. The particulate thermoplastic or mixture may be apolyimide, polyetherimide, polyethersulfone, polyetherketone, or thelike. The amount of such thermoplastic is preferably adjusted to anamount which fails to cause phase separation in the cured matrix resin.Suitable amounts are from 5 to about 30 percent by weight. Preferably,the thermoplastic particles may be described as differentially soluble.Such thermoplastics have a relatively steep rate of solution versustemperature, and may easily be maintained in particulate form duringresin mixing and prepregging, but dissolve rapidly upon cure to producea single phase cured thermosetting resin having a gradient of increasingthermoplastic content which reaches a maximum in the interply region. Athermoplastic may be tested for its differential solubility by simpletests, for example by mixing the requisite amount of thermoplasticparticles with the remaining system components at the mix temperature,followed by heating to the cure temperature for a short time whilestirring. At the mix temperature, the greatest amount of thermoplasticparticles should not dissolve, but remain in particulate form, while atthe cure temperature, the greatest portion should dissolve and anyremaining thermoplastic should at least swell, indicating partialsolubility.

With some matrix resins, differential solubility is not required, but insuch cases it is desirable that the particulate thermoplastic at leastswell in the resin system components, indicating at least somesolubility. In the absence of such behavior, for example with rigidinsoluble thermoplastics such as PEEK and polyvinylchloride, lack ofadherence to the matrix resin may cause increased delamination afterimpact.

Soluble thermoplastics may also be utilized. Such thermoplastics aregenerally added in relatively minor amounts, for example from 5 to about15 percent by weight. Higher amounts of dissolved thermoplasticgenerally leads to undesirable increases in the uncured resin viscosity,which may partially be compensated by use of base resin systemcomponents, i.e. the epoxy, bismaleimide, or cyanate monomers, withlower viscosity. Addition of lower amounts of dissolved thermoplastic,i.e. from 5 to 15 percent by weight, will often assist the toughness ofthe system. Further, when lower amounts of dispersed particulatethermoplastic is utilized, the addition of dissolved thermoplastic cansometimes alter the solvent character of the matrix in such a mannerthat particulate thermoplastics which are normally too soluble, may inthe presence of the dissolved thermoplastic, exhibit the desirabledifferential solubility alluded to earlier.

The preformed, low T_(g), functionalized elastomers are generally addedat temperatures between 50° C. and 150° C., for example at about 100° C.The elastomers are normally added prior to addition of curing agent whenused with epoxy resins, in order to avoid premature advancement of theresin. If particulate thermoplastics are utilized, they may be added atthis time also. However, when dissolved thermoplastics are utilized,they are normally added prior to addition of the elastomer. In somecases it may also prove to be advantageous to prereact the elastomericparticles with the matrix resin at elevated temperatures for an extendedperiod of time, for example 30-150 minutes at 100° C.-150° C. Thechemical reaction between the functional groups of the elastomer and thematrix resin can optionally be accelerated by the use of a suitablecatalyst. It should be noted, however, that the particulate elastomermust not dissolve under these conditions, but must remain in particulateform. Such prereaction is believed to assist in promoting adherence ofthe low T_(g) rubber particles to the resin matrix.

The toughened matrix resin systems of the subject invention may beutilized as neat films in structural adhesives, or may be scrimsupported for these applications. In the case where use as matrix resinsfor fiber-reinforced prepregs is contemplated, the fiber reinforcementmay be in the form of a random nonwoven mat, a woven textile, orunidirectional tows or tape. The fibers utilized may be high meltingorganic fibers or inorganic fibers.

Examples of high melting organic fibers are the high temperaturepolyolefin (e.g. those sold under the tradename SPECTRA® fibers),polyetherketone (PEK) and similar fibers, for example those sold by BASFA. G. under the tradename ULTRAPEK® polyetherketone; all aromaticpolyamides, or aramid fibers; and the like. Preferably, however,inorganic fibers such as glass quartz, carbon (and graphiticmodifications), silicon carbide, boron nitride, ceramic, and the likeare utilized. The toughened matrix resins of the subject inventiondemonstrate their toughness best when utilized with carbon fibers, forexample the intermediate modulus carbon fibers sold under the tradenameCELION® by BASF Structural Materials, and Hercules IM-7 fibers.

Curing of the adhesives and prepregs of the subject invention utilizeconventional cure temperatures and cure cycles. Bismaleimide systems aregenerally cured under modest autoclave pressure at 350° F. (177° C.),for example. In the Examples which follow, the various low T_(g)functionalized elastomers were visually observed to have a particle sizedistribution such that the smallest particles ranged from 1-2 μm insize, the largest particles 50-70 μm in size, and the greatest portionof particles based on weight percent were between 10 and 20 μm.

The invention may be illustrated by the following examples.

EXAMPLE 1--COMPARATIVE

A bismaleimide resin system was prepared by dissolving 54 parts byweight of the bismaleimide of 4,4'-diaminodiphenylmethane intoapproximately 40 parts by weight of 2,2'-diallylbisphenol A at 138° C.After the mixture had cooled, 0.3 parts by weight of triphenylphosphinedissolved in 2,2'-diallylbisphenol A was added. The total amount of2,2'-diallylbisphenol A comonomer in the composition was 46 parts byweight. Prepregs were prepared from the resin system utilizing HerculesIM 7 intermediate modulus carbon fibers. These prepregs weresubsequently laid up in a quasiisotropic panel having a nominal resincontent of 35 weight percent tested for compression strength afterimpact (CAI) according to Boeing support specification 7260 at an impactlevel of 1500 in-lb/in. The panel exhibited a CAI of 22.6 ksi.

EXAMPLE 2

To the resin system of comparative Example 1 was added 5 weight percentof NIPOL® 5045, a 1:1 acrylonitrile/butadiene elastomer containing lessthan 1 weight percent acrylic acid and less than 1 weight percentacrylate ester, and having a T_(g) of -8° C. Prepregs prepared as inExample 1 and laid up into quasiisotropic panels exhibited a CAI of 34.2ksi, a 51 percent improvement over the system of Comparative Example 1.

EXAMPLE 3--COMPARATIVE

Into a resin kettle was introduced 268 grams of o,o'-diallylbisphenol Acomonomer at room temperature. Mixing was commenced with anULTRA-TURRAX® 600 watt mixer as a result of which the temperature of thecomonomer rose to above 38° C. Next, 713 grams of a eutectic mixture ofbismaleimides containing approximately 64 weight percent, 15 weightpercent, and 21 weight percent respectively of the bismaleimides ofmethylenedianiline, trimethylhexamethylene diamine, and toluene diaminewas added using external cooling, when necessary, to keep thetemperature below 93° C. Prior to addition, the bismaleimide had beencoarsely crushed and sieved to a particle size of less than about 3 mm.After the addition of bismaleimide was completed, an additional 20 gramsof diallylbisphenol A containing 5 weight percent of curing catalyst wasadded at a temperature below 82° C. The finished resin system was coatedonto silicone coated release paper and used to prepare a carbon/graphiteprepreg as in Example 1. Microscopic examination revealed no largecrystals of bismaleimide, but disclosed instead a uniform dispersion ofparticles having a size below about 20 μm. The prepregs thus prepared,when laid up into quasiisotropic panels and tested as in Example 1exhibited a CAI of 28.2 ksi.

EXAMPLE 4

To the slurry mixed resin system of Comparative Example 3 was added 5weight percent of NIPOL 5045. Panels prepared from prepregs preparedfrom this resin system exhibited a CAI of 33.7 ksi, an increase of 19percent over Comparative Example 3.

We claim:
 1. A toughened thermosetting bismaleimide resin system,comprising:A. A base resin system comprising(i) one or more bismaleimidefunctional monomers; (ii) a comonomer which is an alkenylphenol; and(iii) optionally, a dissolved thermoplastic having a T_(g) greater than150° C.; B. from about 1 percent to about 10 percent by weight relativeto the total system weight of a functionalized, lightly crosslinkedelastomer having a T_(g) of less than 10° C., and a particle size offrom about 2 μm to about 70 μm; and C. optionally, particulateengineering thermoplastics in an amount of from 10 to 30 weight percentbased on the total resin system weight.
 2. The resin system of claim 1wherein said functionalized elastomer has a T_(g) of less than 0° C. 3.The resin system of claim 1 wherein said functionalized elastomercontains carboxyl, carboxamide, epoxy amine, or anhydride functionality.4. The resin system of claim 2 wherein said functionalized elastomercontains carboxyl, carboxamide, epoxy, amine, or anhydridefunctionality.
 5. The resin system of claim 1, further comprising:D. alow viscosity epoxy resin.
 6. The resin system of claim 5 wherein theresin system contains from about 5 weight percent to about 15 weightpercent of a dissolved thermoplastic.
 7. The resin system of claim 4wherein the resin system contains from about 5 weight percent to about15 weight percent of a dissolved thermoplastic.
 8. The resin system ofclaim 6 wherein said resin system contains from about 5 weight percentto about 30 weight percent of a particulate thermoplastic.
 9. The resinsystem of claim 1 wherein said particulate thermoplastic B is adifferentially soluble thermoplastic.
 10. The resin system of claim 5wherein said particulate thermoplastic B is a differentially solublethermoplastic.
 11. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 1. 12. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 2. 13. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 3. 14. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 4. 15. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 5. 16. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 6. 17. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 7. 18. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 8. 19. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim
 9. 20. A fiber reinforced thermosettable prepregcomprising(a) from 20 to about 80 weight percent of fibrousreinforcement; and (b) from 80 to about 20 weight percent of the resinsystem of claim 10.